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document snappy decompression assumptions

This commit is contained in:
Jacek Sieka 2020-05-14 15:25:01 +02:00 committed by zah
parent a605c7244e
commit 3c98f18d47
1 changed files with 10 additions and 3 deletions
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13
beacon_chain/libp2p_streams_backend.nim
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@ -42,15 +42,22 @@ proc uncompressFramedStream*(conn: Connection,
let
crc = uint32.fromBytesLE frameData.toOpenArray(0, 3)
todo = expectedSize - output.len
remaining = expectedSize - output.len
chunkLen = min(remaining, uncompressedData.len)
# Grab up to MAX_UNCOMPRESSED_DATA_LEN bytes, but no more than remains
# according to the expected size. If it turns out that the uncompressed
# data is longer than that, snappyUncompress will fail and we will not
# decompress the chunk at all, instead reporting failure.
let
uncompressedLen = snappyUncompress(
frameData.toOpenArray(4, dataLen - 1),
uncompressedData.toOpenArray(0, min(todo, uncompressedData.len) - 1))
uncompressedData.toOpenArray(0, chunkLen - 1))
if uncompressedLen <= 0:
return err "Failed to decompress snappy frame"
doAssert output.len + uncompressedLen <= expectedSize,
"enforced by `min` above"
"enforced by `remains` limit above"
if not checkCrc(uncompressedData.toOpenArray(0, uncompressedLen-1), crc):
return err "Snappy content CRC checksum failed"